The detection and quantification of low parts per billion levels of ionic species in water is becoming of increasing importance in a number of processes. For example, in the steam and boiler water used in electrical power plants, ionic species such as sodium, chloride, sulfate, nitrate, phosphate, and potassium can lead to the pitting of turbine blades even when present at only the parts per billion level. In order to analyze for ions present in such minute amounts, a representative sample of the fluid must be collected in a totally inert container and put into a form suitable for the analytical method, avoiding all possibility of contamination. In the case of anions, the sample must be preconcentrated 10 to 100 times in order to bring the sample into the sensitivity range of the best analytical methods. A major problem in analyzing for such low levels of ions is the difficulty in finding an inert container for storing them. Some container materials will contaminate the sample with species leached out of the container walls while other container materials remove trace impurities by irreversible absorption onto the interior surfaces of the container. The storage time required for these sample distortions to occur is largely unknown. Thus, a method for collecting and preconcentrating high purity water samples which avoids the use of containers, minimizes the handling of the sample, concentrates the sample and leaves the concentrated sample in a form compatible with the analytical method to be used would be very desirable.